The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Dry pipe sprinkler systems used in fire protection typically are applied in unheated occupancies and structures that may be exposed to freezing temperatures. The dry pipe system is connected using a differential control valve that will hold back a high pressure water supply against a low pressure air supply that is used in the system to supervise the integrity of the sprinkler system piping. A dry pipe control valve must operate on the loss of air pressure in the system due to operation of a fusible link sprinkler that operates due to a fire condition. The lower air pressure must also hold the dry pipe control valve closed against the higher pressure water supply.
Dry pipe control valves are typically designed as swing type valves including a clapper that pivots about an axis parallel to the flow axis and require ratios of differential areas of the annular water seat to the annular air seat of typically 5.5:1. Also, the friction loss of supply water through the dry pipe control valve is required to meet regulatory parameters that inherently require the valve water supply seat and outer housing to be large. In particular, existing regulations require the low pressure air seat to be 5.5 times larger than the water seat effective area resulting in a very large control valve. The dry pipe control valve is required to be located in a heated portion of the protected building structure where the water supply up to the control valve will not freeze. The system discharge piping is maintained with the required air or gas pressure to keep the dry pipe control valve shut until a fire condition occurs where a fused sprinkler will operate or open due to a rise in temperature above its designed operating temperature. When the sprinkler opens the air pressure within the dry pipe system is lowered to an operation point or pressure of the dry pipe control valve where the water pressure overcomes the air supply pressure and allows the dry pipe control valve to open. At this point, water flows through the control valve to the open piping system and the operated sprinklers and water is thereby discharged on the fire area being protected.
Dry pipe control valves currently used have been of the single swing type clapper design where the pivot point is offset from the center of the concentric annular seat. The air seat is concentric or eccentric from the water seat and a double seat is required, one for supply water and a larger seat for air or gas on the system discharge side of the valve. A space between the air and supply water seat is an intermediate space that maintains atmospheric pressure. The complete clapper must swing upward with the flow of water through the valve. This requires the valve body to be very large compared to the supply waterway to accommodate the large area for the air seat compared to the water seat for the operation of the 5.5:1 differential area (which is an industry standard) and requires a large valve body area for the clapper to swing out of the waterway to prevent large friction losses in a flowing condition. The 5.5:1 differential area ratio is the relationship of the mean air seat annular area divided by the mean water seat annular area. Also in some valve designs the distance to the pivot point of the clapper versus the centerline of the water seat versus the air seat area must also be factored in to the differential ratio. In the case of a current differential dry pipe control valve design for a 6″ diameter water seat valve using a 5.5 ratio (industry standard) the air seat is required to have a 14 inch diameter and the valve body must be larger to accommodate the body wall, proper clearances and assembly flanges. This makes the dry pipe control valve very large, heavy and difficult to install.
In another application, fire protection deluge or flow control valves are applied where the system discharge piping and discharge devices are open (or possibly closed) and air or gas is used to supervise the piping for preaction systems. The valves are smaller, using a lower differential to hydraulically maintain the valve closed and using the supply water pressure for supplying a priming pressure to a back side of the valve for holding the valve closed, and the air or gas is connected through a releasing device connected to a smoke, flame or heat detection and releasing control system. In the event of a fire, the detection system sends a signal to a release control panel that signals a solenoid valve to open and thus releases the priming pressure from the hydraulic actuator that latches the main deluge or flow control valve closed. In this type of fire protection valve currently in use, a clapper and diaphragm directly in line with the annular seat and piping inlet is applied with the priming supply pressure on the top of the actuator that is larger than the supply seat by typically a 2:1 ratio. As the liquid priming pressure is released, the hydraulic force on the clapper or actuator is released and the valve unlatches, in a swing-type valve, or the clapper rises to allow flow through the valve. For the swing-type clapper the valve only opens full or closes with no control of the flow. In the diaphragm-type clapper where the clapper moves vertical to open, and supply liquid flows past to an outlet, the upper prime chamber pressure can be regulated to maintain a desired position of the clapper to control the flow of the discharge liquid or to automatically close the valve when desired. In this type of valve, the pressure loss is typically high and the valve body must be large to accommodate the maximum allowed pressure loss required by the industry.
Eccentric rotating plug valves are currently used in the process industry where operation is continuous and regulations of operation are based on hydraulic or pneumatic actuators or on manual actuation. The eccentric rotating plug valves typically include a separate motive system source other than the system being controlled. The actuator force utilized to seal the plug and seat is maintained with a pneumatic actuator or hydraulic system with the actuator rotating the plug and forcing the plug into the annular seat to result in a sealed tight connection. Most eccentric rotating plug valves require very tight tolerances to maintain a positive seal over time and numerous operations.
In fire protection valves, the pressure loss through the system control valve is regulated. Also, the operating torque for an efficient plug valve must be low, in order to maintain accurate control of the actuator for operation due to loss of system pressure while using the supply liquid of the system to open the valve. Use of eccentric plug valves where the plug rotating shaft centerline is offset from the seat centerline allows for a longer lasting plug and seat due to elimination of scrubbing of the seal surfaces during opening and closing of the valve. This typically requires close tolerances of the plug to seat and centerline locations to consistently maintain a proper seal on the valve. In addition to the close tolerance requirements, the load on the seat must be constant to maintain the seal of the seat and plug, with the load coming from an actuator or manual lever that is latched. Where external actuators and control systems are applied, the operating torque of the plug valve is not critical to operation due to the potential of power applied from the external actuator sources.
For fire protection valves, the control of opening the clapper or rotating plug for the subject valve is critical to the consistent operation over the life of the valve installation and for the variable system operating pressures provided. Also, fire protection valves are installed and put in service for many years and only operate a couple times each year for verification of operation and proper leak tight sealing. These operating conditions are difficult to account for in a control valve design due to corrosion and brackish water combined with the presence of air in the fire protection systems.
Rotating plug valves currently applied in the process industry typically operate continuously and are less susceptible to sticking or corroding closed. Also, they do not typically use the flow medium they control as the mechanism for operation. Fire protection deluge or dry pipe valves are required to operate when a fire occurs and are non dependent on external power sources. A fire protection control valve must operate based on the potential of fire in all situations even in non controlled situations where the only power available to operate the systems comes from the liquid supply and the loss of supervisory pressure in the discharge system piping.
Generally, eccentric rotating plug valve designs include a fixed annular seat and plug seal where rotation of the plug along with a rotational force generates the sealed connection between the annular seat and the solid plug in the liquid passage of the valve housing.